Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $196.85   12.736%   $221.9208   $221.92   $221.90   $221.90  
  Purchase #2 $20.35   3.254%   $21.0122   $21.01   $21.00   $21.00  
  Purchase #3 $221.32   3.133%   $228.254   $228.25   $228.25   $228.30  
  Purchase #4 $119.57   6.609%   $127.4724   $127.47   $127.45   $127.50  
  Purchase #5 $236.39   4.606%   $247.2781   $247.28   $247.30   $247.30  
  Purchase #6 $155.73   5.265%   $163.9292   $163.93   $163.95   $163.90  
  Purchase #7 $41.59   11.423%   $46.3408   $46.34   $46.35   $46.30  
  7 purchase totals = $991.80       $1,056.2075   $1,056.20   $1,056.20   $1,056.20